June 13, 2017

Team Turtle's forecast discussion:

"Summary:
Let's be wheels up at 8 am with an Aberdeen, SD preliminary target/base camp. Expect dryline to initiate by late afternoon and semi discrete storms tracking toward the warm front draped south of I-94 east southeast into western MN.

Discussion:
Evening model guidance suggests a rich plume of upper 60's lower 70's dews advecting northward along the MO River into the eastern Dakotas. A warm front pushing north toward I-94 in eastern ND and a dryline draped SSW across eastern SD into central NE with Mid to lower 60's dews along the dryline to the south. Given more robust moisture to the north, ample backing of winds along the surface low in northern SD and along the warm front, and midlevel flow of 50 knot southwesterlies, I'd expect the dryline to light up by late afternoon, storms to organize in a strongly destabilized warm sector and hopefully produce for us this evening as they approach the warm front where surface winds back and SRH is quite pronounced.

Further south. Mean flow paralleling the dryline suggests storm coverage and mode might be an issue. We've also got some high T/Td spreads with surface temps in the low 90s forecast and dews in the low to mid 60s. CAM guidance suggests the dryline erupting in a rather solid squall. Timing is a little off on the midlevel speed max down there.

For tornadoes, the north end of this setup sounds like the much stronger target. Lets make for Aberdeen. We can adjust from there if we need to run up to Jamestown, ND or east on highway 12 toward 29. Beautiful gridded chase terrain up there too provided it's not flooded, but I haven't heard of any up there. If we can get there by 20z or so. We should have time to adjust. So departure at 13z, 7 hours-ish to get up there with a stop or two for fuel, and then an hour or two to adjust as needed for a 22z-01z chase."

We plodded our way north up highway 83 through Valentine, NE to Murdo, SD then through Pierre, cutting east toward Faulkton, and Mellette, which is just south of Aberdeen. We arrived in Mellette with just enough time to refuel before the dry line to our southwest exploded with rapidly organizing supercells. We raced south and then west to Rockham for the intercept. A tornado warning was issued before we arrived. We got right in the notch to see a large wall cloud and long tail cloud extending out from a green rear flanking core. It was a beastly, menacing storm, but I was a bit dismayed to see it already in a high precipitation state immediately upon our arrival. That’s one of the downsides of chasing the warm front with rich boundary layer moisture: an HP storm mode is often favored.

A huge shelfy forward flank gust front extended from south to north just to our west and was closing in fast. It was super dramatic, tinged in green, but it would keep us on our toes avoiding severe weather in the menacing core.

We were most interested where this long lowered line of cloud intersected the large, circular rear flank gust front to our south. That’s where our chances would be best for spotting a tornado if it wasn’t buried in the core. We did not sight one before the core forced us to start moving east, however.

Tornado reports started to come in as we drove. It was indeed buried in the rear flank core to our south. We couldn’t confirm at our position at the time, but Anton’s cameras did indeed capture the rain wrapped cone tornado.

We scooted east ahead of the storm, the low contrast funnel visible on the far right side of the image here. But the tornado never emerged from the rain and our visibility of it never improved before it finally disappeared altogether.

We continued east several miles toward Redfield, trying to maintain our position just ahead of the inflow notch. The rear flank gust front bowed outwards with a lot of turbulent motion and scud. It didn’t look promising for a tornado, but the storm surprised us anyway. A length of occluded gust front extending behind the main bowing RFD gust front started to curl and wrap up. A prominent cone funnel formed in the middle of the compact cylindrical swirl. We had just enough time to radio the development to Anton, turn off the highway, and then point the cameras at it before it condensed.

The tornado was a tiny rope, produced by one of the most compact tornado cyclone wall clouds I’ve seen. The lighting was exquisite, however, foreground scenery and background storm evenly lit with nice shading and color on funnel and clouds. Brindley was ecstatic with the catch.

The rope funnel danced at the ground for a bit, and then retreated. It was fully condensed for mere seconds only, and hidden among the chaotic motion of the huge parent supercell. It was as if the storm was trying to hide its secret treasure from prying eyes, but we got in there at just the right moment and angle to capture the fleeting spectacle.

The tornado cyclone spun strongly for a while after the tornado dissipated, but it appeared that was the last gasp of the storm. The rear flank gust front continued to bow as if the storm was gusting out. We tracked with it through Redfield, but as the tornado warnings were dropped, we finally decided to let the storm go and target new, developing updrafts to the southeast. They looked like discrete supercells initially but by the time we arrived, they were quickly merging into a large severe line. We stair stepped to stay ahead of the core for as long as we could, but our chess game chase finally ended with the storm catching us at checkmate. We had no east option and the line ran us over. We turned our cars to face into the hurricane like winds as we were battered in the core with torrential sheets of rain and hail approaching severe threshold. It was exhilarating to experience the storm, but it pretty much meant our chase was over. We had no new supercell targets within strike range and would now be behind the developing squall line.

We decided to call the chase and make for the nearest town with grub open late and a room: Mitchell. We converged at The Depot, an old converted train station, for some fried food and chase stories.

Storms receded to the east with golden sunset mammatus. It was a gorgeous end to a great chase.